Do you enjoy grapefruit juice, frappuccinos or candy made from black licorice? If so, be sure to read your medication bottles. Many prescription and over-the-counter drugs react with these foods. To avoid serious – and possibly dangerous – side effects, here are 9 common food and drug interactions to watch out for…

Next time your doctor prescribes a new medication, don’t forget to ask if you need to change your diet.

“Eating certain foods while taking certain drugs can change the medication’s effectiveness, so you may get more or less than prescribed,” says Barbara Mendez, R.Ph., M.S., a New York-based pharmacist and nutritional consultant.

Foods can also magnify drug side effects or create entirely new ones, she adds.

For example, soy decreases the effectiveness of thyroid drugs. Grapefruit juice intensifies the side effects of antihistamines, so you’re likely to get the jitters. Combine black licorice with a prescription diuretic like Lasix, and you could lose too much potassium and suffer dangerous irregular heart rhythms, according to the Food and Drug Administration (FDA).

Reactions can be severe or even deadly, the FDA reports. That’s where reading the fine print on the drug packaging is a must.

Also, "consumers should talk with their [doctors] about how to lower the risk of interactions," advises Shiew-Mei Huang, Ph.D., deputy director of the Office of Clinical Pharmacology at the FDA's Center for Drug Evaluation and Research (CDER).

A 2009 study conducted by Prescription Solutions, a leading pharmacy benefit management organization and a UnitedHealth Group company in Irvine, Calif., found that 54% of Americans don’t consistently take prescriptions as instructed, which may increase the risk of food and drug interactions.

To reduce your risk, “make sure your doctors and pharmacists know all the drugs you’re taking, including over-the-counter sleep aids, diet pills, laxatives, diuretics, and vitamin and herbal supplements, all of which can interact with food as well as other drugs,” says Harris Cohen, M.D., a Philadelphia-based physician and medical advisor for Epocrates.com, a San Francisco-based company that publishes medical and drug software.

Other steps include the following:

Fill all your prescriptions at the same pharmacy, preferably one with a computerized system for flagging potential problems.

Keep a list of your medications and allergies in your wallet for easy access, recommends Jennifer Kingdon, Pharm.D, a pharmacist with Prescription Solutions.

1. AlcoholNever take any drug with alcohol, which reacts with more than 50 prescription drugs, increasing or decreasing their effectiveness, advises Carlos Reynes, M.D., a board-certified internal medicine physician certified in integrative medicine who specializes in pharmaceuticals with Loyola University Health System's Gottlieb Memorial Hospital in Illinois.

That’s because alcohol’s enzymes can cause dangerous medication interactions, transforming some drugs into poisons that can damage your liver or other organs. Alcohol also magnifies the sedative effect of tranquilizers, sleeping pills and narcotic drugs.

Medication interactions with alcohol: Antibiotics(Furoxone, Flagyl and other antibiotics that treat infection): May cause nausea, vomiting, headache and convulsions.

Anticoagulants (Coumadin [warfarin] and other drugs that prevent abnormal blood clotting): Increases the amount of these drugs in your bloodstream, raising the risk of life-threatening hemorrhages.

Antidepressants(tricyclic antidepressants such as Elavil; selective serotonin reuptake inhibitors, or SSRIs, like Celexa and Lexapro; and MAOI inhibitors like Nardil and Marplan): Just one drink can increase an antidepressant’s sedating effects and cause a dangerous rise in blood pressure.

Diabetes medications(Orinase, Glibenclamide and others that lower blood sugar levels): Decreases the effectiveness of these drugs, and causes nausea and headache.

Antihistamines(over-the-counter meds like Benadryl, Allegra, Claritin, as well as prescription antihistamines like Hyzine and Periactin that treat seasonal allergies and insomnia):Intensifies the sedating effect of these drugs and may cause dizziness.

Anti-seizure medications(Dilantin and others that prevent epileptic seizures):May make these drugs less effective in protecting against epileptic seizures.

Gastrointestinal medications(Tagamet, Zantac):Increases the levels of these drugs and increases side effects like headache, dizziness and nausea.

Blood pressure medications:(Aldomet, Apresoline and others that treat high blood pressure and angina): Reduces the drugs’ efficacy and may cause dizziness and fainting.

Narcotic pain relievers(Darvon, Demerol, morphine and codeine that treat severe pain):A single drink can increase the sedative effects of these drugs and cause coma or even death.

Acetaminophen (Tylenol): Combined with alcohol,even small doses of acetaminophen can cause liver damage and stomach bleeding.

Sedatives and hypnotics(tranquilizers like Valium, anxiety medications like Ativan, and benzodiazepine sleeping pills like Dalmane and Restoril):Increases sedative effects, such as drowsiness, and could lead to coma or fatal respiratory conditions.

2. Grapefruit juice and grapefruitThe cells that line your small intestine contain an enzyme called CYP3A4, which helps break down many medications. Grapefruit juice contains a substance that inhibits this enzyme, causing medication interactions, like increasing the levels of the medication in your bloodstream.

All in all, grapefruit juice reacts with more than 50 medications, says Mendez. Here are the most common:

Stimulants(drugs like epinephrine and pseudoephedrine found in over-the-counter cold and flu meds like Sudafed and Nyquil, and in some diet pills and herbal remedies): Caffeinated beverages increase heart rate and high blood pressure.

Asthma medications(albuterol, Beclomethasone and other drugs that make it easier to breathe): Increases irritability, jitteriness, heartbeat, nausea and headache.

Tyramine is an amino acid that occurs naturally in foods and the body. It helps regulate blood pressure and may reduce the effects of certain antidepressants, according to the FDA. It increases in foods that are fermented, pickled, aged or stored for several days at room temperature or in the freezer.

Medication interactions with high-tyraminefoods: MAOI (Monoamine oxidase inhibitors)(Emsam and others): Tyramine reduces the effectiveness of these depression treatments and may cause dangerously high blood pressure.For a list of foods to avoid, see this chart from Vanderbilt University. Among foods you may safely enjoy:

“Young” cheeses like cottage, ricotta and farmer’s, but not aged ones.

Fresh, canned or packaged – but not frozen – meat, poultry or seafood.

Dairy products, but not cultured products like sour cream, buttermilk and yogurt.

5. Foods high in vitamin K Vitamin K, which is abundant in leafy greens and cruciferous veggies, is essential for blood clotting, but interacts with many drugs. So ask your physician if you should reduce your intake of any vegetables.

Medication interactions with vitamin-K rich foods: Anticoagulants (drugs like warfarin and Coumadin that treat high blood pressure and abnormal blood clotting): Vitamin K reduces the effects of these drugs and may cause high blood pressure, bleeding and bruising.

6. Dairy products, high-calcium foods and calcium supplementsYou need 1,000 mg of calcium if you’re under age 51 and 1,200 mg if you’re 51 or older, according to the Institute of Medicine, an arm of the National Academies of Science. But too much of the bone-building mineral can bind with some medications and decrease their effectiveness, warns Kingdon.

Medication interactions with high-calcium foods:Thiazide diuretics (Aquatensen, Diucardin and others that lower blood pressure): High doses of calcium taken with thiazide diuretics can cause milk-alkali syndrome, which shifts the body’s acid-base balance toward alkalinity and can lead to kidney failure.

Tetracyline (Robitet, Tetra and others that treat bacterial infections): Even small servings of dairy products, including milk, cheese, yogurt and ice cream, will decrease the antibiotic’s effects.

7. High-potassium foods (bananas, oranges, leafy greens, salt substitutes with potassium): Potassium works with sodium to maintain your body's water balance. But combining potassium-rich foods with hypertensive medications can lead to potassium overload, causing rapid or irregular heartbeat, according to the FDA.

Medication interactions with high-potassium foods:Potassium-retaining diuretics (Triamterene and other diuretics that treat hypertension by lowering the kidney’s ability to excrete potassium): Taking these drugs with potassium-rich foods can overload your system.

8. Black Licorice Black licorice contains the compound glycyrrhizin, which can increase the risk for irregular or rapid heartbeat and heart attacks when eaten in excess. It may also cause sodium and water retention, low potassium and high blood pressure. When combined with diuretics, licorice can lead to potassium deficiency.

“Black licorice is the only kind of licorice that contains glycyrrhizin,” Mendez advises. “Eat red licorice – or ditch the sugar altogether and have a handful of nuts.”

Medication interactions with black licorice:ACE-inhibitors (Lanoxin, Altace, and others that regulate blood pressure and prevent heart attacks):Lowers the effectiveness of these drugs and increases birth defects during the third trimester of pregnancy.

Thiazide diuretics (Hydrodiuril, Aldactone and other potassium-sparing diuretics that lower blood pressure): Reduces the effectiveness of these drugs and increases side effects like nausea, dizziness and photosensitivity (sensitivity to sunlight).

Digoxin (Lanoxin and other drugs used to prevent heart failure and stroke): May increase side effects like nausea, vomiting, headache, loss of appetite and diarrhea.

Soy contains goitrogens, compounds that may interfere with thyroid function if your diet is also low in iodine, according to a 2000 report by the FDA. This was first discovered years ago when a large percentage of Asian women (who regularly eat soy) became more likely to develop hypothyroidism.

Medication interactions with soy:Thyroid medications (Synthroid, Armour Thyroid, Thyrolar and other thyroid meds that correct hypothyroidism, or an underactive thyroid): Soy decreases the effectiveness of these medications. If you’re not a vegetarian, save soy for special occasions. If you’re a vegan or vegetarian who relies on soy as a protein source, talk to your physician about adjusting your thyroid medication dose, advises the NCL.

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